Manufacture of viscose rayon



MANUFACTURE F VISCOSE RAYON August Briitz, Kurt Richter, Wilhelm Wachtendorf, and

Kurt Heuer, all of Erlenbach (Main), Germany, as- I signors to American Enka Corporation, Enka, N.C., a corporation of Delaware No Drawing. Filed Feb. 18, 1957, Ser. No. 640,6171

Claims priority, application Germany Feb. 20, 1956 4 Claims. (c1. 1s-s4 Z a 'This invention relates to the production of regenerated cellulose articles such as'fibers, films and the 'like from viscose.

More particularly this invention relates to the production of said articles having substantially all skin area, high strength and high fatigue rei sistance. A need for a very high tenacity viscose rayon yarn [exists inthe industry today in order to compete with "other synthetic fibers.

--s'u.itab1e for tire cord or other industrial cords high tenacity and long flex life.

In recent times, research has been directed toward ever increasing the strength and improving other physical properties of viscose rayonrequiring It is known that a definite relationship exists between -'the strength of rayon yarn and the skin structure of the yarn.

. paratively thick skin in contrast to the older types, of

textile rayons which have a very thin skin. As a general 5 rule, the strength of the yarn increases as the percentage of skin. area increases and the percentage of core decreases.

Furthermore, it is known that yarns havri-ing a large degree of skin have a lower swelling value as 2 compared to yarn of little or no skin.

The skin and core as referred to herein are not different types of material but occur from the same stream of viscose. However, it has been established that the orientation and crystallinity of the cellulose molecule The formation of a yarn having a considerable de- I gree of skin area may be influenced in ditferent ways.

For example, viscose rayon yarns which have a -relatively thick skin may be produced by regenerating the cellulose in the presence of a viscose additive which modifies the regeneration-coagulation process of the visc'ose 'in the acid spinbath.

Among the viscose modifiers known today are those compounds disclosed in British Patent No. 741,728, U.S.

.. Patents Nos. 2,535,044, 2,535,045, 2,536,0l4 and 2,69,6,423. A large number of other such additives are" also in the literature.

Although in some instances these viscose modifiers exert a. favorable and pronounced'infiuenee upon the ;:;physical properties of the yarn produced in their pres- .ence, however, from an operational point of view it jjis not very desirable to use modifiers in the process for the production of viscose rayon. Great difliculty .::is, usually encountered when viscose modifiers are used.

--'*the mount of additive, especially in the spinbath.

In the first place, it is exceedingly difficult to control It the additive is permitted to build up in the spinbath, the

efiect of the additive in manycases notably decreases;

and in some cases, an inferior yarn will be produced.

Rayons of the high tenacity type have a com-.

. 2,947,597 Patented Aug. 2., 1960 The undesirable buildup may occur from the fact that the effect of the modifier is dependent upon being incorporated in the viscose. Also, certain additives are decomposed by the acid and accordingly present difficult removal and spinning problems. Furthermore,

the spinbath in the viscose process is constantly being spent in operation and must be regenerated by adding fresh sulphuric acid and removing the excess sodium sulphate. Regeneration of spinbath containing these additives present many operational problems. Thus, it would be desirable to operate without the additives Also, by varying the spinningconstants a yarn of varying degrees of skin thickness may be produced. By varying the acid concentration the skin thickness can be increased by either increasing or decreasing the acid concentration depending upon other spinning constants.

It is known that in general increasing the salt content of the spinbath, as well as lowering the temperature of the spinbath, influences the production of yarn with increased skin thickness. Also, the viscose may be varied to influence skin formation such as increasing or decreasing the sodium hydroxide content, decreasing the aging of the viscose, increasing the amount of CS used during xanthation and increasing the cellulose content thereof.

It is interesting to note that the various factors are interrelated but their effects are not necessarily additive.

Although the general idea of varying the coagulationregeneration process conditions to produce viscose rayon yarn with some skin is old, the problem of selecting the optimum spinning conditions is by no means simple. Up to the present it was considered that a yarn having :.over 50% skin could not be produced without sacrificing other yarn properties unless a viscose modifier is employed. Furthermore, unmodified skin filaments heretofore produced have peripheries which are highly crenulated. 7

Also, in the art today it is known that by varying the spinning conditions and without spinning in the infiuence of a modifier, yarns which have a dry strength of only slightly more than 3 grams per denier can be produced. In view of the present demand for high strength yarn, these strength values are very inadequate. However, when the known optimum spinning conditions are employed, it is necessary to take undesirable steps in the production of the the yarn, for example, the use of high CS concentrations in the .xanthation.

A very high strength yarn may be produced by the so-called Lilienfeld process in which viscose is extruded into a coagulating bath containing sulphuric acid generally in the amount of -70% by weight. The spinning or coagulation bath treatment may be followed by a secondary bath also having a relatively high sulphuric acid content. However, other physical properties are not improved and, in most instances, are poorer. Theyarn produced by the Lilienfeld process is very brittle and is almost worthless for use in articles which require good extensibility and good fatigue resistance.

While the above-mentioned known methods for producing a yarn having high strength and a high degree of skin represent valuable advances in the art, further improvements in the yarn properties without at the same time presenting spinning problems are needed.

In accordance with the present invention, viscose having sodium hydroxide in the amount of 6% or less by weight and a maturity of about 4046 gamma number is spun into a coagulating spinbath containing about 17-19% sodium sulphate, 45-60% sulphuric acid, and zinc sul- Q phate, the concentration. of which is dependent upon the concentration. of the sulphuricacid. It is preferred that v the ratio of the acid content to the zinc sulphate content be 1.2408 to 1. After a short travel through the spinbath, the freshly spun. yarn is directed into a second hot 7 weakly acid bath where the yarn is stretched in the .con-

values are in the region of only 70%. The most remarkable. fact is that the cross-section of the yarns reveals filaments which, have at least 80% skin and which have peripheries of notably reduced crenulation. Also, the yarns. have enhanced. abrasion and fatigue resistance values.

7 enema? to give a viscose solution viscosity of 50- 60 .poises ,was xanthated in the usual manner with 37% CS The itemthate thus obtained was dissolved with caustic soda solution to provide a viscose which contained 7.3% cellulose and 5.5% NaOI-I. After aging to a maturity of 42 gamma number, deaerating and filtering, the viscose was extruded in a spinbath which contained 4.9% H SO 17.1% Na SO and 5.0% ZNSO The coagulating bath had a temperature of 62 C. and the spinneret employed was of the conventional type and had 720 orifices, each orifice having a diameter of 60 microns. g

The freshly spun yarn was directed throu'ghthe' spinbath for a distance of 17 cm. and out of this first'bath into a: second bath. In this second bath which contained 2% H SO and had a temperature of 90 C., the yarn was given a stretch of 90%. The drawo'lf speedof the yarn was 60 meters per minute. Later the yarn was aftertreated in the usual manner, such as Washing, desulphurizing, drying, etc. However, before finally drying the yarn was given an additional stretch of 3-l0%' The dried thread was given a twist of I20 turnsper meter.

The physical properties of 1650 denier yarn produced in the above manner were as follows. In. the dry state Itis. important to the present invention that the percentage of sodium hydroxide in the viscose benot. more than 6%. There appears to be no defined lower value for the percent caustic. Generally, it is preferred that thealkali content be no lower than 4.5. However, a. viscose with even a lower alkali may be used. In any case/the sodium hydnoxid'e should be sufficiently high to render the viscose amenable tozthe conventional filtering and-spinningprocesses. The maturity of the viscose is not critical in: the

pnesent invention. But it: is preferred that the viscose be aged to aa ripeness of about 4046 gamma number.

AnLsonit' is. importantthat the concentration of materials in the spinbath. be maintained between certain defined ranges- It is necessary that the sulphuricv acid be kept at 4.5.-.6.0.%. Above 6.0% thev skin. thickness of the-yarn notably decreases, below 4.0% many spinningproblems? arise. The. concentration of salts in the spinbath should be. maintained at. certain levels in order to retaintheir skin formation effect. For example, the optimum concentration of sodium sulphate in the present invention is l 7-l'9%:. depending upon the amount of acid in the spinbath. 'It has been established that the optimum concentration of the zinc salt is reached when the ratio of acid to zinc salts is 1.2-0.8 to 1. In other words, when'the acid level is 425% the smallest concentration of zinc sulphate should. be'about' 3.8%; and when the acid level is 6.0% the respect to the cellulose and alkali contents of the viscose and the constituents of the spinbath, with ordinary commercial spinning employing at least 7.0% sulphuric aicd. It has'now been recognized that a commerciallyuseful I viscose rayon process may be employed at relatively low concentrations of acid when the viscose composition andthe composition of the sulphuric acid coagulating bath are so balanced to permit the production of regenerated cellulose filaments having improved tenacity, flex life and'characterizedv by an exceptionally high degree of skin. 7

The process may be more fully illustrated by reference I to the followingexamples which are not to be construed as limiting the present invention in any respect;

Example I I Alkali cellulose prepared from cotton linters and aged The concentration of zinc sulphate is varied) the strength or the yarn was 435 g./100 denier and the elongation was 7.8%. In the conditioned state" the strength of the yarn was 291 g;/ 100 denier and the" elongation; was 24.4%. The swelling value of the yarii 70.9%.

Exam'p'le II In order to illustrate the critical balance of the spinning variables and to show how the yarn propertiesiare affected thereby, experiments were run using conditions other'thanthe preferred conditions of the present invention. In this respect it was found that the desirable yarn properties of the present. invention were not obtainable. Also, thetskin area of the yarn was considerably less.

For example, viscose prepared in. identical manner asiin Example'l-wasextruded into a spinbath' containing 6.5%

- I-I'gSO4, -l7.5-% Na SO and 3.5% ZnSO Other spinning conditions and aftertreating: of the thread'wasthe" same as described in Example I. The physical propertieesof yar n produced were 35O-g./1-00 denier dry strength; 10.0%

dr'ye'longation, ZlO'g/IOO denier wet strengthaand 22 0% wet elongation.

What is claimed is:

1. A'process for the production of regeneratedcellulose articles having substantially all skin fromviscose comprising spinning a solution consisting essentially" of viscose containing sodium hydroxide in the amount of less 6% by weight into acoagulating spinbath consisting essentially of 1 7-19 sodium sulphate, 45-60% sulphuric acid, andzinc sulphate, directing the spunarticle out of said spinbathinto a second bath containing dilute sulphuric-acid, and stretching the spun article; in the second bath to an extent of at least the concentration of zinc sulphate being adjusted so that the ratio of sulphuric acid insaid spinbath to zinc sulphate is 142-08 2. A process for the production of regenerated cellulose articles having substantially all skin froni vi'scose comprising; spinning a solution consisting es's'enti'ally Qof "viscose containing 4.5'-6.0% by weight of sodium hydioxide into a coagulatingspinbath. consisting essentially co'nsistingf essentially of viscosecontaining-4.59550 by :3 weight of sodium hydroxide into a coagulating spinbath consisting essentially of 17-19% sodium sulphate, 4.5- 6.0% sulphuric acid, and zinc sulphate, directing the spun yarn out of said spinbath into a second bath containing about 2% sulphuric acid and having a temperature of about 90 C. and stretching the yarn in the second bath at least 85%, the concentration of zinc sulphate being adjusted so that the ratio of sulphuric acid in said spinbath to zinc sulphate is 12 0.8 to 1.

UNITED STATES PATENTS Cox Dec. 26, 1950 Cox Dec. 26, 1950 FOREEGN PATENTS Australia Mar. 8, 1956 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No, 2,941,597 August 2 1960 August Brcitz et ale It is hereby certified that error appears in theprinted specification of the above numb ered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 50, for "less 6%" read less than 6% Signed and sealed this 31st day of January 1961 (SEAL) Attest:

KARL H AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

1. A PROCESS FOR THE PRODUCTION OF REGENERATED CELLULOSE ARTICLES HAVING SUBSTANTIALLY ALL SKIN FROM VISCOSE COMPRISING SPINNING A SOLUTION CONSISTING ESSENTIALLY OF VISCOSE CONTAINING SODIUM HYDROXIDE IN THE AMOUNT OF LESS 6% BY WEIGHT INTO A COAGULATING SPINBATH CONSISTING ESSENTIALLY OF 17-19% SODIUM SULPHATE, 4.5-6.0% SULPHURIC ACID, AND ZINC SULPHATE, DIRECTING THE SPUN ARTICLE OUT OF SAID SPINBATH INTO A SECOND BATH CONTAINING DILUTE SULPHURIC ACID, AND STRETCHING THE SPUN ARTICLE IN THE SECOND BATH TO AN EXTENT OF AT LEAST 85%, THE CONCENTRATION OF ZINC SULPHATE BEING ADJUSTED SO THAT THE RATIO OF SULPHURIC ACID IN SAID SPINBATH TO ZINC SULPHATE IS 1.2-0.8 TO
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